Wednesday, July 13, 2016

This film is a time-lapse summary of many of the features Olbinski photographed this spring while chasing weather for 18 days and 20,000 miles over a period of two months. He records many "spinning" features in the atmosphere: rotating mesocyclones, roll clouds, tornadoes, downpours, dust, and churning skies. The film is dramatic and awe-inspiring, and the music by Kerry Muzzey gives the film an epic feel.

As for the title of the film, vorticity is a clockwise or counterclockwise spin in the troposphere. We typically look at vorticity at the 500 millibar level, which is about 20,000 feet. If you have followed this blog you have seen vorticity depicted on some of the 500 millibar maps I've included, like this one. The orange and yellow shading depict areas of vorticity, spinning that produces upward motion, and thus usually clouds and precipitation.

Wednesday, July 6, 2016

The I-79 Clendenin exit in Kanawha County, WV, on June 24, 2016.Credit: Facebook/West Virginia Department of Transportation

Two weeks ago Friday residents of West Virginia woke up to a disaster in the making. Heavy thunderstorms trained over the mountainous terrain of southeastern West Virginia dumping almost ten inches of rain in less than 12 hours over parts of two counties.

The flooding washed out many roads, caused landslides, destroyed numerous bridges, and left behind a thick layer of mud and debris in many communities. The death toll from this flood stands at 26, making it the third most deadliest flood in the state's history. In the days following the flood at least 32,000 homes and businesses were without power and more than 60 secondary roads in the state were closed.

The Elk River soared to a record crest of 33.37 feet on the morning of June 24, rising about 27 feet above the level it was on June 23.

Heavy rain occurs frequently during this time of the year in many parts of the country, but why was this particular event the disaster it was?

Geography plays a big part. The topography of West Virginia is mountainous, and the steep hills and long narrow valleys are conducive to flooding in very heavy rain events, particularly in the southeastern part of the state. In this particular situation, the heavy rain fell in a relatively short period of time (hours, not days) rushed down the hillsides and was funneled down the valleys. Rivers rose quickly and in some cases cut off escape routes.

The second major factor were training thunderstorms - thunderstorms that repeatedly move over the same area. There were actually two rounds of rain that moved across the state, but the second round that occurred beginning on the afternoon June 23 was the straw that broke the camel's back.

The surface weather map at 8:00 a.m. on June 23 showed a cold front extending from a low over Indiana through the Midwest, and a warm front extending east from the low through Ohio and Pennsylvania.

8:00 a.m. EDT June 23, 2016

By 8:00 p.m. on June 23 the front extended from Missouri east into southern Ohio. It stalled out there as a series of low pressure waves rippled along the boundary. These ripples along with warm, humid air south of the front was the ingredients needed for the heavy rain.

8:00 p.m. EDT June 23, 2016

As of 12:30 a.m. on June 23 there were only a few thunderstorms developing in western West Virginia, with most of the activity further north along the front.

However, during the pre-dawn hours thunderstorms rapidly developed and were producing some heavy rain. Showers and thunderstorms continued during the morning hours.

By late afternoon and evening thunderstorms were numerous and oriented west to east across central and southern West Virginia. There was only a slow southward advancement so the thunderstorms essentially trained across the same area.

By 10:30 p.m. EDT the line of storms finally pushed south, leaving widespread flash flooding in their wake.

Counties outlined in green are under flood warnings.

Nicholas and western Greenbrier Counties in West Virginia received the most rain, though heavy rain also occurred in western Virginia and flood warnings were issued for several counties there. Radar estimated up to 10 inches in Greenbrier County, with up to seven inches falling in only three hours.

24-hour rainfall ending at 8:00 a.m. EDT on June 24

36-hour rainfall amounts end the morning of June 24, 2016

Measured amounts included 8.29 inches in White Sulphur Springs and 8.00 inches in Lewisburg, both in Greenbrier County. The CoCoRaHS observer at Runa 0.1 W in Nicholas County measured 7.20 inches of rain. 24-hour amounts this high have one a 1 in 1000 probability of occurring (0.1 percent).

Credit: NWS Blacksburg, VA

Fifteen of the fatalities occurred in Greenbrier County. Damage was extensive. The Greenbrier GolfClassic scheduled to start July 7 was canceled. The President declared central and southeast West Virginia major disaster areas.

Below are two links that contain slideshows of the flooding and damage in West Virginia and Virginia.